This disclosure relates in general to polarization sensitive sensors and, but not by way of limitation, to lateral viewing and polarization maintaining sensing devices amongst other things.
Tissue birefringence can be used as a diagnostic tool for tissue state, such as damage, and tissue identification. Tissue birefringence is the result of protein structure anisotropy, such as found in collagen, configured in a highly organized cellular matrix. The birefringence is the result of geometrical organization of the local index of refraction of the various tissue structures and tissue components. This inhomogeneity in refractive index provides spatial gradients in refractive index (n), as a result the light propagation in either forward (transmissions) or backward (backscattered) direction reveals spatial variations in intensity.
Prior studies in biological samples have found the effects of dichroism to be minimal in skin and muscle tissue, and have focused on measurement of retardation due to birefringence for contrasting different types of tissue and assessing the severity of burns. Tissue birefringence can be determined by probing tissue with light of known polarization state and measuring the changes in the polarization state after the light propagates through the tissue.
Optical coherence tomography (OCT) is a technique for in-vivo microscopy which obtains micron-scale cross-sectional images of subsurface structure in biological tissues. While conventional OCT measures the depth-resolved reflectivity profile of backscattered light, polarization-sensitive OCT (PS-OCT) systems have been developed to add the capability of controlling the polarization state of light incident upon the sample and measuring the reflectivity of light returning in particular polarization states. Such selectivity allows for the measurement of birefringence and/or dichroism. PS-OCT systems avoid the polarization artifacts that often occur in conventional OCT images of birefringent samples.
Most conventional OCT systems use non-polarization-maintaining (PM) single-mode fiber interconnections because they are inexpensive, allow for easy alignment and handling, and enable flexible sample arm designs which are important for in vivo measurements such as surgical and endoscopic applications.
PS-OCT systems use light of known polarization to image a target. In many applications, the target is located within vessel or small cavity and may be located on the wall of the target. As such, probes or sensors with forward sensing or forwarding probing may not accurately image the vessel or cavity wall. These challenges are also found in industrial applications as well as various medical applications.